Method and device for the continuous production of hydrogen sulfide

ABSTRACT

The invention relates to a process and to an apparatus for preparing hydrogen sulfide H 2 S by converting a reactant mixture which comprises gaseous sulfur and hydrogen over a solid catalyst. The reactant mixture is converted at a pressure of from 0.5 to 10 bar absolute, a temperature of from 300 to 450° C. and a sulfur excess in a reactor ( 1 ). The sulfur excess corresponds to a ratio of excess sulfur to H 2 S prepared of from 0.2 to 3 kg of sulfur per kg of H 2 S prepared.

The invention relates to a process and to an apparatus for continuouslypreparing hydrogen sulfide H₂S by converting a reactant mixture whichcomprises gaseous sulfur and hydrogen over a solid catalyst.

In the prior art, hydrogen sulfide is prepared, for example, by the H₂Sprocess according to Girdler (Ullmann's Encyclopedia of IndustrialChemistry, Sixth Edition, 2003, Vol. 17, page 291). In this process, H₂Sis prepared in a non-catalytic manner from the elements sulfur andhydrogen in a column with internals and an essentially horizontallyaligned, extended bottom. Hydrogen is introduced into the bottom filledwith boiling sulfur, and strips sulfur into the ascending gas phase.Hydrogen and ascending sulfur react in the gas space of the column, andthe heat of reaction released is withdrawn from the product gas bywashing with liquid sulfur. To this end, liquid sulfur is drawn off fromthe bottom of the column, mixed with fresh cold sulfur and introduced atthe top of the column. The product gas, which comprises substantiallyhydrogen sulfide, is cooled in two heat exchangers. A disadvantage isfound to be that the process has to be performed under pressure and atelevated temperature. The elevated temperature leads to increasedcorrosion rates and material attrition on the reactor walls. In the caseof a leak, relatively large amounts of poisonous H₂S escape owing to theelevated pressure. It is also disadvantageous that the product stillcomprises considerable amounts of unreacted hydrogen (3% by volume) andof further impurities (2% by volume).

GB 1,193,040 relates to a process for preparing H₂S from the elements atelevated temperature and elevated pressure. The reaction is performed ina column with internals, the hydrogen being supplied at the lower end ofthe reactor and excess molten sulfur at the upper end of the reactor.The reaction proceeds at a temperature of from 400 to 600° C.(preferably from 450 to 540° C.) and a pressure of from 4 to 15 atm(preferably from 5 to 12 atm). A disadvantage is the high temperaturewith regard to corrosion and the pressure for safety reasons.

U.S. Pat. No. 5,173,285 relates to a process for preparing hydrogensulfide by reacting sulfur and hydrogen. The preparation is effected intwo stages at an elevated pressure of from 0.3 to 30 kg/cm², preferablyfrom 3 to 30 kg/cm², and a temperature between 250 and 600° C.,preferably from 300 to 450° C. A disadvantage is the high pressure usedin the embodiments described. A further disadvantage is the residualhydrogen content of 3.2% in the product gas.

DE 3 437 010 A1 has for its subject matter a process for preparinghydrogen sulfide from the elements. The preparation is effected in aflame at temperatures between 650 and 1300° C. The starting substances,sulfur and hydrogen, are used in a molar ratio of from 0.8 to 1.2:1,preferably in a stoichiometric ratio. A disadvantage in this process isthe high temperature, which leads to increased corrosion of the plant.

FR 2 765 808 A1 is based on a further process for preparing hydrogensulfide under pressure and at temperatures from above 350° C. to 465° C.over a catalyst with an excess of hydrogen using a double-tubecountercurrent evaporator for the sulfur. In this process, the hydrogenis heated by the H₂S stream from the reaction stage. The hot hydrogenreleases its heat to the sulfur stream and is mixed into the sulfurwhich is conducted into the heat exchanger space. A portion of the H₂Sis recycled in order to prevent the sulfur from building up excessivelyhigh viscosities with hydrogen. A disadvantage is the relatively highlevel of apparatus complexity as a result of the double indirectheating. First, H₂S heats the hydrogen. Then, the hydrogen heats thesulfur. A further safety disadvantage is operation under high pressure(>10 bar in the example).

U.S. Pat. No. 2,214,859 relates to a process for preparing hydrogensulfide. The preparation is effected at a sulfur excess of from 4:2 to1.5:2 (ratio of atomic sulfur:atomic hydrogen). The synthesis reactionis performed at from 500 to 800° C. over a catalyst comprising oxides orsulfides of cobalt, nickel or molybdenum. A disadvantage is the highenergy consumption of the process as a result of lack of utilization ofthe heat of reaction. A further disadvantage is the high temperatures atwhich the reaction is performed, which lead to increased corrosion.Another disadvantage is that the conversion of the hydrogen is a maximumof 98%.

A catalytic preparation of H₂S is described in Angew. Chem.; volume 74,1962; 4; page 151. In this preparation, hydrogen is passed through anexternally heated sulfur bath. The hydrogen laden with sulfur vaporpasses through bores into a catalyst space, Unreacted sulfur, afterleaving the catalyst space, is condensed in an upper part of the H₂Soutlet tube and passes via a return tube back into the sulfur bath. Thecatalyst space is arranged concentrically about the H₂S outlet tube. Adisadvantage in the process on the industrial scale is that the heat ofreaction is not utilized to heat the sulfur bath, but rather the heatingis effected through the jacket of the sulfur bath.

DE 1 113 446 discloses the catalytic preparation of hydrogen sulfide byconverting a stoichiometric mixture of hydrogen and sulfur over acatalyst comprising cobalt salt and molybdenum salt on a support attemperatures between 300 and 400° C. The catalyst is arranged in tubeswhich are flowed through by the mixture of hydrogen and sulfur. Thesulfur bath has a temperature of from 340 to 360° C., as a result ofwhich a stoichiometric mixture of hydrogen and sulfur is generated bypassing hydrogen through the sulfur bath for the preparation of H₂S. Theheat of reaction released in the H₂S formation is utilized by directheat exchange, since the tubes comprising the catalyst are arranged inthe sulfur bath in a manner not described in detail. In long-termoperation, the process according to DE 1 113 446 does not achievecomplete conversion of the hydrogen.

Further processes for preparing hydrogen sulfide are described, forexample, in CS 190792 and CS 190793, although no statements are maderegarding the pressure in the reactor during the synthesis reaction. Afurther preparation process is explained in Ullmann's Enzykiopäadie dertechnischen Chemie [Ullmann's Encyclopedia of Industrial Chemistry], 4thedition, volume 21, page 171.

It is an object of the present invention to provide a process and anapparatus for preparing hydrogen sulfide, which avoid the disadvantagesof the prior art. In particular, it is an object of the invention toprovide a process and an apparatus which enable a virtually completeconversion of the hydrogen and/or the attainment of a hydrogen sulfidepurity in the crude gas stream obtained in the synthesis of ≧99.5% byvolume in long-term operation.

According to the invention, this object is achieved by a process forpreparing hydrogen sulfide H₂S by converting a reactant mixture whichcomprises gaseous sulfur and hydrogen over a solid catalyst. Thereactant mixture is converted at a pressure of from 0.5 to 10 bar(preferably from 0.75 to 5 bar, more preferably from 1 to 3 bar, mostpreferably from 1.1 to 1.4 bar) absolute, a temperature of from 300 to450° C. (preferably from 320 to 425° C., more preferably from 330 to400° C.) and a sulfur excess in a reactor. The sulfur excess correspondsto a ratio of excess sulfur to H₂S prepared of from 0.2 to 3 kg(preferably from 0.4 to 2.2 kg, more preferably from 0.6 to 1.6 kg, mostpreferably from 0.9 to 1.2 kg) of sulfur per kg of H₂S prepared.

As a result of the combination of the parameters selected within theranges mentioned in the preparation of hydrogen sulfide, a purity of thecrude gas stream obtained in the synthesis reaction (once the excesssulfur has been separated out in a cooler) of at least 99.5% by volumeis achieved in long-term operation of the reactor. A sulfur excess aloneis not sufficient to achieve a hydrogen sulfide purity of at least 99.5%by volume (as stated, for example, by U.S. Pat. No. 2,214,859). Forvirtually complete conversion of the hydrogen, a sulfur excess of ≧0.2kg of sulfur per kg of H₂S obtained is employed. Excesses of more than 3kg of sulfur per kg of H₂S are economically unviable.

Surprisingly, the parameter combination used in the process according tothe invention (in spite of low temperatures of from 300 to 450° C.) canachieve virtually complete conversion of the hydrogen (<0.5% by volumein the H₂S-containing crude gas stream) in long-term operation, withoutthe sulfur excess resulting in higher stress on the catalyst.

The present invention has the advantage that hydrogen sulfide can beobtained from hydrogen and sulfur with high purity and high processreliability in a simple apparatus construction with a one-stagereaction. The synthesis reaction is performed at relatively lowtemperatures at which only low corrosion rates are present. The lowpressures are advantageous for safety reasons. The low pressure causes,for example, only low leakage rates in the event of leaks at flanges.The process according to the invention enables energy-efficientpreparation of hydrogen sulfide.

In a preferred embodiment of the present invention, the catalystprovided comprises particles which comprise at least one elementselected from the group of Ni, W, Mo, Co and V (preferably Co and Mo) inoxidic or sulfidic form on a support composed of alumina or silica. Thereaction of the gaseous reactants more preferably takes place over acatalyst comprising Co and Mo as the active component on alumina as asupport. The use, for example, of a Co—Mo catalyst allows sufficientreaction rates to be achieved at comparatively low temperatures (<450°C.) and pressures (especially <1.5 bar absolute). The catalyst ispreferably used for the present invention in the form of a fixed bed ofbulk material. It is possible to use shaped bodies of any shape. Thecatalyst may, for example, be present in the form of cylindrical orstar-shaped extrudates.

For example, the diameter of the shaped bodies is from 2 to 12 mm, inparticular between 3 and 10 mm, more preferably between 4 and 8 mm, andthe length is preferably between 2 and 12 mm, in particular between 3and 10 mm, more preferably between 4 and 8 mm. The catalyst loadings inthe process according to the invention are preferably from 0.08 to 1standard m³, preferably from 0.13 to 0.8 standard m³, more preferablyfrom 0.18 to 0.6 standard m³, most preferably from 0.22 to 0.4 standardm³ of hydrogen per hour and per kg of catalyst. Standard m³ refers tothe gas volume at 0° C. and 1.013 bar absolute.

In a preferred embodiment of the present invention, the conversion ofthe reactant mixture is performed in a one-stage reaction. In thiscontext, one-stage reaction means that the majority of the hydrogenprovided as a reactant is converted in a single reactor. The conversionof the majority means that at least 80%, preferably at least 90%, morepreferably at least 95%, most preferably at least 99%, of the hydrogenis converted in the reactor. A one-stage reaction in a reactor (forexample a tube bundle reactor) without a postreactor allows a simpleapparatus construction to be realized. Preference is therefore given toperforming the process according to the invention only with a one-stage(not with a multistage) conversion of sulfur and hydrogen

Moreover, in the process according to the invention, the saturation ofthe reaction mixture with sulfur is preferably effected in one stage andnot a plurality of stages, in order to keep the reaction structuresimple.

In a preferred embodiment of the present invention, heat of reactionwhich arises in the conversion of the reactant mixture is utilized forevaporation of the sulfur. This achieves an energy-efficient process.The heat of reaction is preferably supplied to a sulfur melt by at leastone of the following processes which provides sulfur for the reactantmixture:

-   A) arranging the catalyst in at least one (preferably U-shaped)    tube, the reactant mixture being converted in the tube and the tube    being partly in contact with the sulfur melt,-   B) heating gaseous hydrogen via a heat exchanger by means of thermal    energy of an H₂S-containing crude gas stream obtained in the reactor    in the conversion of the reactant mixture, and passing the heated    hydrogen through the sulfur melt, and-   C) utilizing the thermal energy of the H₂S-containing crude gas    stream obtained in the conversion of the reactant mixture by means    of a heat exchanger to heat the sulfur melt.

In variant A), the reaction tube which comprises the catalyst over whichthe reaction is performed is positioned in the sulfur melts. Inconnection with the present invention, “being in contact” means that aheat exchange can take place between the sulfur melt and the interior ofthe tube through the wall of the tube. The at least one (preferablyU-shaped) tube is preferably immersed partly into the sulfur melt.

A process according to variant B) can be performed, for example, asdescribed in FR 2 765 808. The product (H₂S-containing crude gas stream)releases energy via a heat exchanger to hydrogen, which then heats thesulfur.

In variant C), it is also possible that the hot H₂S-containing crude gasstream releases heat via a heat exchanger directly to the sulfur.

In a preferred embodiment of the present invention, the reactant mixtureis obtained by passing gaseous hydrogen through a sulfur melt into areactant region of the reactor, the sulfur melt having a temperature offrom 300 to 450° C., preferably from 320 to 425° C., more preferablyfrom 330 to 400° C. As a result, sulfur is stripped by the hydrogen outof the sulfur melt into the gas phase to obtain the reactant mixture.The heat of reaction released in the exothermic reaction of H₂Sformation from hydrogen and sulfur preferably evaporates the liquidsulfur from the sulfur melt in the reactor. The evaporation of thesulfur is preferably supported by stripping with gaseous hydrogenintroduced simultaneously into the sulfur melt, which bubbles throughthe liquid sulfur. The evaporation rate of the sulfur is adjusted inaccordance with the invention such that the H₂S synthesis reaction isperformed with a sulfur excess, the sulfur excess corresponding to aratio of excess sulfur to H₂S prepared of from 0.2 to 3 kg, preferablyfrom 0.4 to 2.2 kg, more preferably from 0.6 to 1.6 kg, most preferablyfrom 0.9 to 1.2 kg, of sulfur per kg of H₂S prepared.

It is also possible to recycle a portion of the H₂S-containing crude gasstream into the liquid sulfur. The recycled hydrogen sulfide can be usedto strip sulfur into the gas phase. It can also serve to reduce theviscosity of the sulfur which is to be converted in the reaction.However, preference is given to a process without recycling ofH₂S-containing crude gas in order to ensure a simple apparatusconstruction.

In a preferred embodiment of the present invention, an H₂S-containingcrude gas stream passed out of the reactor is cooled in a cooler(preferably to from 114 to 165° C.) to separate out excess sulfur, andsulfur obtained in the cooler is recycled into the reactor for thepreparation of H₂S.

The H₂S-containing crude gas stream passed out of the reactor preferablyhas a temperature of from 290 to 400° C. The excess sulfur is condensedout at least partly in the cooler. The cooling medium used may, forexample, be pressurized water at 120° C. in a secondary circuit. Thesulfur obtained in the cooler is preferably recycled into the reactorfor preparing H₂S. To this end, the sulfur may be recycled by means of aspecial collecting and diverting construction into the sulfur melt inthe jacket space of the reactor. The cooler used for the presentinvention is preferably a tube bundle heat exchanger.

Preference is given to providing a line between the cooler and thereactor, through which the crude gas stream is passed in one directionfrom the reactor into the cooler and through which the recycled sulfuris passed in an opposite direction from the cooler into the reactor.

The invention further relates to an apparatus for continuously preparinghydrogen sulfide H₂S, comprising

-   -   a reactor for converting a reactant mixture comprising gaseous        sulfur and hydrogen over a solid catalyst at a pressure of from        0.5 to 10 bar (preferably from 0.75 to 5 bar, more preferably        from 1 to 3 bar, most preferably from 1.1 to 1.4 bar) absolute,        a temperature of from 300 to 450° C. (preferably from 320 to        425° C., more preferably from 330 to 400° C.) and a sulfur        excess which corresponds to a ratio of excess sulfur to H₂S        prepared of from 0.2 to 3 kg (preferably from 0.4 to 2.2 kg,        more preferably from 0.6 to 1.6 kg, most preferably from 0.9 to        1.2 kg) of sulfur per kg of hydrogen sulfide prepared, and    -   a cooler which is connected to the reactor and is for cooling an        H₂S-containing crude gas stream passed out of the reactor to        condense at least a portion of the sulfur excess,        a line being arranged between the reactor and the cooler for        passing the crude gas stream in a direction from the reactor        into the cooler and for recycling sulfur in an opposite        direction out of the cooler into the reactor. The inventive        apparatus is preferably used to perform the process according to        the invention.

The sulfur condensed out of the H₂S-containing crude gas stream in thecooler can, for example, return to the reactor at the bottom of the sametube through which the H₂S-containing crude gas stream is conducted outof the product region of the reactor into the cooler. This allows anadditional recycle line to be avoided. This simplified pipeline designhas the advantage, among others, that it is possible to dispense withtwo flanges which would constitute possible leakage sites from which thehighly poisonous hydrogen sulfide could emerge. A further advantage isthat the common line acts like a countercurrent heat exchanger in whichthe returning sulfur cools the hydrogen sulfide. The cooler can thus bedesigned for a lower cooling output. The returning sulfur cools thehydrogen sulfide actually directly downstream of entry into the productregion of the reactor, so that the product region is protected fromexcessively hot gas zones and hence from corrosion.

It is surprising that sulfur which emerges from the reactor at, forexample, 350° C., which is already of low viscosity again, and sulfurwhich returns at, for example, 120° C. and is not yet highly viscous canbe conducted past one another in counter-current without highly viscoussulfur at 200° C. blocking the connecting tube. Although it is knownthat the sulfur coming from the reactor is saturated with H₂S and thatH₂S reduces the viscosity of sulfur by about a factor of 100, thiscannot be considered to be sufficient.

In a preferred embodiment of the present invention, an H₂S-containingcrude gas stream cooled by the cooler is passed through activated carbonpresent in a vessel at a temperature between 114 and 165° C. (preferablyfrom 127 to 162° C., more preferably from 135 to 160° C.) and sulfurwhich is obtained is collected in the bottom of the vessel.

Polysulfanes (H₂S_(x) where x≧2) may be present as impurities in theH₂S-containing crude gas stream. These form, for example, within aparticular temperature range in the course of cooling of a hotH₂S-containing crude gas stream which is passed out of a reactor inwhich the H₂S synthesis is effected. Above 350° C., H₂S_(x) is unstableand decomposes to sulfur and H₂S. In the temperature range from approx.200 to 290° C., H₂S in the crude gas stream reacts with S to giveH₂S_(x). At temperatures below 170° C., H₂S_(x) formation does not playa significant role.

The polysulfanes present in the H₂S-containing crude gas stream shouldnot precipitate in the course of cooling in the plant used to preparethe H₂S and should not decompose to sulfur and H₂S after a certainresidence time, since sulfur deposits would be the consequence.Therefore, the H₂S-containing crude gas stream and the polysulfanespresent therein are preferably passed through activated carbon in thevessel provided therefor, and the activated carbon acts as a catalystfor the controlled conversion of polysulfanes to H₂S and sulfur. In thevessel comprising the activated carbon, sulfur is therefore obtainedfrom the conversion of the polysulfanes, and entrained sulfur dropletsor a sulfur excess provided for the synthesis may additionally occur inthe crude gas stream.

Entrained sulfur droplets and the sulfur excess are, however, preferablyseparated out in a cooler connected upstream of the vessel.

The crude gas stream is preferably passed through the activated carbonat temperatures from 114 to 165° C., preferably from 127 to 162° C.,more preferably from 135 to 160° C. The holding of the temperature ofthe gas stream above 114° C. during the flow through the activatedcarbon ensures that the sulfur obtained (from the H₂S_(x) decompositionand, if appropriate, from the residual gas stream) remains in the melt.As a result of the holding of the temperature of the gas stream below165° C., the viscosity of the sulfur saturated with H₂S remainssufficiently low. This allows the sulfur obtained to runoff out of theactivated carbon (for example an activated carbon bed) and pass into thebottom of the vessel comprising the activated carbon. The sulfurcollected in the bottom can be recycled to the preparation of H₂S(preferably into the reactor used for the H₂S synthesis).

As a result of the continuous removal of the sulfur from the vesselcomprising the activated carbon, the activated carbon is barely ladenwith sulfur, if at all. An exchange of the activated carbon is thereforeonly rarely necessary, if at all, so that a low consumption of activatedcarbon is achieved and disposal costs and environmental damage, forexample in the case of combustion of the carbon, can be substantiallyavoided. Moreover, it is possible to dispense with a second vesselcomprising activated carbon, to which it would be necessary to switch inthe event of exchange of the activated carbon in the first vessel. Therecycling of the sulfur obtained in the vessel into the synthesisreaction allows the raw material consumption to be lowered.

The sulfur obtained in the vessel comprising the activated carbon ispreferably collected in the bottom of the vessel and recycled into thesynthesis reaction indirectly via the cooler or directly into thereactor.

In the vessel comprising the activated carbon, any activated carbonknown to those skilled in the art is usable, especially activated carbonproduced from wood, bituminous coal, peat or coconut shells. Itpreferably comprises activated carbon particles in a size of from 2 to15 mm, preferably from 3 to 5 mm. The activated carbon may, for example,be present in the form of small cylinders having a diameter of 4 mm. Thepore volume of the activated carbon is preferably more than 30 cm³100 g.The inner surface area of the activated carbon is preferably >900 m²/g,more preferably >1100 m²/g. The activated carbon may comprise one ormore activated carbon types. For example, a first layer composed of afirst activated carbon type and a second layer arranged thereon andcomposed of a second activated carbon type may be used in the activatedcarbon vessel.

The H₂S-containing crude gas stream is preferably passed through thevessel comprising the activated carbon with a superficial residence timeof from 1 to 200 s, preferably from 2 to 100 s, more preferably from 5to 80 s, most preferably from 10 to 50 s. The superficial velocity ispreferably from 0.01 to 1 m/s, preferentially from 0.02 to 0.5 m/s, morepreferably from 0.04 to 0.3 m/s, most preferably from 0.05 to 0.2 m/s.The pressure in the vessel comprising the activated carbon is preferablyfrom 0.2 to 20 bar, preferentially from 0.4 to 10 bar, more preferablyfrom 0.8 to 6 bar, most preferably from 1 to 5 bar absolute. At theentrance to the vessel, a gas distributor device comprising deflectingplates, inlet tubes and/or perforated inlet tubes may be provided inorder to distribute the crude gas stream within the vessel.

In a preferred embodiment of the present invention, the inventiveapparatus comprises a reactor for continuously preparing H₂S by reactinga reactant mixture which comprises essentially gaseous sulfur andhydrogen over a catalyst, the reactor comprising a sulfur melt in alower part of the reactor, into which gaseous hydrogen can be passed bymeans of a feed device. The catalyst is arranged (preferably as a fixedbed) in at least one U-shaped tube which is partly in contact with thesulfur melt, the at least one U-shaped tube having at least one entryorifice arranged above the sulfur melt in a limb through which thereactant mixture can enter the U-shaped tube from a reactant region ofthe reactor, having a flow path within the at least one U-shaped tubealong which the reactant mixture can be converted in a reaction regionin which the catalyst is arranged, and the at least one U-shaped tubehaving at least one exit orifice in another limb through which a productcan exit into a product region (separate from the reactant region).

The reactor preferably comprises a cylindrical or prism-shaped centralbody surrounded by a reactor jacket which is closed at each end by ahood. The hoods may each have any suitable shape, for example be ofhemispherical or conical shape.

The reactor is preferably filled with a sulfur melt in a lower part.Gaseous hydrogen can be introduced into the sulfur melt through a feeddevice, in which case a reactant mixture comprising essentially gaseoussulfur and gaseous hydrogen collects above the sulfur melt in a reactantregion which is in contact with the sulfur melt via a phase boundary andwhich is delimited at the top preferably by a subdivision, for exampleby a plate. In a preferred embodiment of the present invention, theplate is connected to the reactor jacket in an upper part of thereactor, preferably in the upper third, more preferably in the upperquarter, of the reactor interior.

In the reactor used with preference, at least one U-shaped tube which isat least partly in contact with the sulfur melt is provided. The reactoris therefore designed as a kind of tube bundle reactor with catalysttubes which are in a U-shaped configuration. Such a U-shaped tube hastwo limbs which are connected to one another by a curved region at theirlower end. The U-shaped tubes may each have limbs of different lengthsor preferably the same length. The U-shaped tubes may have, for example,a limb diameter between 2 and 20 cm, in particular between 2.5 and 15cm, more preferably between 5 and 8 cm. The at least one U-shaped tubeis preferably arranged vertically in the reactor, the curved regionbeing disposed at the bottom and the two ends of the limbs at the top.

Within the at least one U-shaped tube, preference is given to arranginga catalyst for converting hydrogen and sulfur to H₂S, as a result ofwhich a reaction region is provided. In connection with the presentinvention, the reaction region refers to that region within the U-shapedtubes in which the catalyst is disposed. The reactants are convertedmainly in the reaction region which comprises the catalyst. Theprovision of a reaction region in U-shaped tubes allows a compact designof the reactor with regard to the reactor length, since the reactionregion provided for the reaction of hydrogen with sulfur to give H₂S canbe divided on the two limbs of one U-shaped tube each. Use of thecatalyst allows the conversion to H₂S to be performed at moderatetemperatures and at low pressure. The catalyst is preferably arranged inthe at least one U-shaped tube in the form of a fixed bed of bulkmaterial.

In the preparation of hydrogen sulfide using the preferred embodiment ofthe reactor, the reactant mixture enters from the reactant region into alimb of the at least one U-shaped tube through at least one entryorifice. The entry orifice is arranged in a limb of the at least oneU-shaped tube above the sulfur melt. The entry orifice opens from thereactant region into one limb of the U-shaped tube. The distance betweenthe phase boundary of the sulfur melt and the entry orifice of theU-shaped tube is selected such that a minimum amount of liquid sulfur isentrained in the form of droplets with the stream of the reactantmixture into the interior of the U-shaped tubes. The distance betweenentry orifice and phase boundary of the sulfur melt is preferablybetween 0.3 and 3 m, in particular between 0.6 and 2.5 m, morepreferably between 0.9 and 2 m.

In the preparation of hydrogen sulfide using the preferred embodiment ofthe reactor, the reactant mixture flows through the U-shaped tube alonga flow path, i.e. it flows first, after entry through the entry orifice,through one limb of the U-shaped tube from the top downward, enters thesecond limb through the curved region of the U-shaped tube and thenflows through the second limb from the bottom upward. The reactantmixture is converted mainly in the reaction region which is presentwithin the U-shaped tube, over the catalyst arranged there. Through anexit orifice in the second limb of the U-shaped tube, the gas comprisingthe product enters a product region (which is preferably arranged abovethe sulfur melt and above the reactant region in the reactor), which isseparated from the reactant region (for example by a plate).

Gaseous hydrogen and liquid sulfur are fed to the reactor preferably viaa suitable feed device. At a suitable point, the hydrogen sulfideproduct, for example at an upper hood, is passed out of the productregion of the reactor.

The two limbs of a U-shaped tube are preferably each connected to aplate of the reactor at their upper end, the plate in turn being securedsuitably in an upper part of the reactor on the reactor jacket. Theplate subdivides the reactor preferably into two subregions; inparticular, it determines a product region above it. The preferredsecuring of the at least one U-shaped tube on a plate connected to thereactor jacket allows thermal longitudinal changes of the reactor and ofthe U-shaped tubes independently of one another, since the U-tube bundleis secured on the jacket of the reactor only via the plate, so that itis possible to dispense with compensators in the construction of thereactor. The connection of the U-shaped tubes to the plate at the upperends of their limbs advantageously achieves the effect that the tubesbecome stabilized according to gravity.

In a preferred embodiment of the present invention, a plate whichdivides the reactor interior into a lower subregion below it and anupper subregion above it is arranged in an upper section of the reactor,preferably close to the upper hood.

The upper subregion preferably comprises the product region, whichcomprises mainly the hydrogen sulfide product during the operation ofthe reactor. In each case one limb of the U-shaped tubes is an openconnection with the product region.

The lower subregion of the reactor preferably comprises the reactantregion directly below the plate and, below it, a sulfur melt into whichliquid sulfur is fed from an external source and/or as reflux. Some ofthe U-shaped tubes are in thermal contact with the sulfur melt; some ofthem are preferably arranged directly within the sulfur melt, i.e. areimmersed into the sulfur melt. A transfer of the heat energy released inthe exothermic reaction to give H₂S thus takes place via the at leastone U-shaped tube into the surrounding sulfur melt. The heat of reactionis utilized for an evaporation of the sulfur present therein. Thisthermal coupling enables an energetically favorable process in whichexternal heat supply can be reduced considerably or is not necessary. Atthe same time, overheating of the catalyst can be avoided, whichincreases the lifetimes of the catalyst.

For a good transfer of the heat energy, preference is given tominimizing the heat resistance of the catalyst bed in the reactionregion. For the conversion of the reactants to H₂S, preference is givento providing a multitude of catalyst-comprising U-shaped tubes, so thatthe particular path from the core of the catalyst bed to the wall of thetube is low. A ratio of the sum of the cross-sectional areas of allcatalyst tubes (or all limbs of the U-shaped catalyst tubes) based onthe cross-sectional area of the (preferably cylindrical) reactor body ispreferably between 0.05 and 0.9, especially between 0.15 and 0.7, morepreferably between 0.2 and 0.5, most preferably between 0.25 and 0.4.

In order that there is sufficient thermal contact for the heat transferfrom the U-shaped tube into the surrounding sulfur melt, the aim is thatfrom 20 to 100% of the outer jacket area of a particular U-shaped tubealong the reaction region comprising the catalyst is in contact with thesulfur melt. In order that the heat transfer into the sulfur meltfunctions efficiently, wherever the reaction takes place in the U-shapedtube, the outer jacket area of the U-shaped tube along the reactionregion comprising the catalyst should be surrounded by the sulfur meltto an extent of more than 20%, preferably to an extent of more than 50%,more preferably to an extent of more than 80%. In the case of too low afill level of the sulfur melt in the reactor and hence too low a contactof U-shaped tube and sulfur melt, there is the risk that the heat ofreaction is not removed sufficiently.

In flow direction of the reactant mixture, within the at least oneU-shaped tube, the reactant mixture, after entry into the U-shaped tube,can first flow through an inert bed, in which case any entrained liquidsulfur present in the form of droplets is separated out of the reactantmixture at this inert bed. For example, a proportion of liquid sulfur inthe reactant mixture comprising gaseous hydrogen and sulfur of up to 100000 ppm by weight may be present. For the separating-out of the sulfurdroplets, a proportion of the inert bed, based on the overall bedcomposed of inert bed and catalyst bed, of from 1 to 30%, especiallyfrom 2 to 25%, preferably from 5 to 20%, more preferably from 8 to 16%,is preferably provided in the at least one U-shaped tube. The inert bedmay consist of bodies of any shape, for example of saddles or preferablyof spheres which are composed of a suitable material, for examplezirconium oxide or preferably aluminum oxide.

Preference is given to introducing gaseous hydrogen into the sulfur meltin the reactor by means of a feed device and to distributing it by meansof a distributor device.

The feed device preferably comprises a tube which is open at both endsand is arranged vertically in the reactor, and which is arranged belowthe distributor device and whose upper end projects preferably into thespace which is defined by the distributor plate and the edge whichextends downward, into the hydrogen bubble. Projection into the spacebelow the distributor plate and especially into the hydrogen bubbleformed below it advantageously prevents inhomogeneous hydrogenintroduction into the sulfur melt.

An inlet tube which runs obliquely, through which the hydrogen isintroduced from outside the reactor, preferably opens into the verticaltube of the feed device. The feed device is advantageously configuredsuch that sulfur which enters the tube arranged vertically can flowfreely downward without blocking the feed device for the hydrogen. Thehydrogen rises upward within the tube arranged vertically and collectsbelow the distributor device.

The distributor device preferably comprises a distributor plate which isarranged horizontally in the reactor and has passage orifices and anedge extending downward. The preferably flat distributor plate extendspreferably virtually over the entire cross-sectional area of thereactor, a gap remaining between reactor jacket and distributor device.The gap between the edge of the distributor device and the reactorjacket preferably has a width between 1 and 50 mm, in particular between2 and 25 mm, more preferably between 5 and 10 mm. The shape of thedistributor plate is guided by the geometry of the reactor in which itis arranged. It may preferably have a circular or polygonal shape or anyother desired shape. Recesses may preferably be provided on the outercircumference of the distributor plate, which provide passage orifices,for example, for hydrogen introduction, sulfur introduction and sulfurrecycling. The gap between distributor device and reactor jacket maythus have only a small width, so that severe vibration of thedistributor device in the reactor is avoided. The hydrogen introducedbelow the distributor device accumulates below this distributor plate toform a hydrogen bubble in the space which is defined by the edgeextending downward and the distributor plate. The distributor plate ispreferably arranged horizontally in the reactor, so that the hydrogenbubble which accumulates below the distributor plate has virtuallyconstant height. As a result of the passage orifices in the distributorplate, the accumulated hydrogen is dispersed with uniform distributionfrom the hydrogen bubble into the sulfur melt disposed above of thedistributor plate. The number of passage orifices in the distributorplate is guided by factors including the volume flow rate of thehydrogen introduced and is preferably from 2 to 100, especially from 4to 50, more preferably 8 to 20, per 100 standard m³/h. The passageorifices may, for example, be circular or defined as slots, preferreddiameters or slot widths being from 2 to 30 mm, preferably from 5 to 20mm, more preferably from 7 to 15 mm. The passage orifices are preferablyarranged regularly in the distributor plate. The areal proportion of thepassage orifices, based on the area of the distributor plate, ispreferably between 0.001 and 5%, preferentially between 0.02 and 1%,more preferably between 0.08 and 0.5%.

In order to ensure good mixing of the sulfur melt by the ascendinghydrogen and thus to ensure very efficient stripping of the sulfur intothe ascending hydrogen, the gas velocity of the hydrogen dispersed bythe passage orifices is preferably from 20 to 500 m/s, especially from50 to 350 m/s, preferably from 90 to 350 m/s, more preferably from 150to 250 m/s.

When there is penetration of sulfur into the passage orifices, whichsolidifies within the passage orifices, especially in the case oflowering of the temperature, the hydrogen distribution at thedistributor device through the passage orifices is inhibited. Theaccumulated hydrogen can then also disperse into the sulfur melt via theedge region of the edge which extends downward, in which case thehydrogen from the hydrogen bubble is then distributed within the sulfurmelt present in a gap between distributor device and reactor jacket. Theedge region of the distributor device is preferably configured inserrated form, as a result of which the hydrogen accumulated below it isdistributed in fine gas bubbles.

In the case of simple introduction of hydrogen, for example, via avertical inlet tube without such a distributor device into the sulfurmelt, an inhomogeneous hydrogen distribution can arise. In the vicinityof the inlet tube, large bubbles of hydrogen rise within the sulfurmelt. In other regions of the sulfur melt, there is then barely anyhydrogen. As a result, vibrations of the U-shaped tubes can be induced.The distributor device which is preferably present in the inventivereactor and is configured like a bell open at the bottom therefore alsoserves to stabilize the U-shaped tubes of the tube bundle in thepreferred embodiment of the reactor.

In order to achieve greater stability of the U-shaped tubes, the atleast one U-shaped tube may be connected to the distributor device closeto its lower curved region, said distributor device limiting thevibration region of the U-shaped tube or of the corresponding tubebundle in the horizontal direction through its dimensions. In this case,the distributor device is in turn not connected directly to the reactorjacket of the reactor, but rather is connected indirectly to the reactorjacket via the connection of the U-shaped tubes to the plate. As aresult, problems due to stresses between reactor, U-shaped tubes anddistributor device caused by the thermal changes in length are avoided.

In one embodiment, the distributor plate is connected to the particularlimbs of the at least one U-shaped tube close to the lower end of theU-shaped tube, for example welded, a section of the U-shaped tube whichcomprises at least part of the curved region being disposed below thedistributor plate. Since this section of the U-shaped tube is not incontact with the sulfur melt but rather projects into the region of thehydrogen bubble accumulated below the distributor device, the U-shapedtube in this section preferably does not comprise any catalyst bed.There is thus no conversion to H₂S and no exothermic heat of reaction tobe removed arises. Within the at least one U-shaped tube, subdivisionsmay be provided, which separate the region of the catalyst bed from theregion without bed, although the subdivisions have to be permeable forreactants and products for the H₂S preparation.

In the present invention, a feed device and a distributor device forgaseous hydrogen are preferably provided in a lower section of thereactor, for example close to the lower hood. The hydrogen introducedinto the sulfur melt by means of the feed device rises in the form ofgas bubbles distributed by the distributor device through the melt,which strips sulfur out of the melt, and accumulates (for example belowan upper plate of the reactor) in the reactant region of the reactor asa reactant mixture which is in contact with the sulfur melt via a phaseboundary.

The process according to the invention for continuously preparing H₂Scomprises the conversion of a reactant mixture which comprisesessentially gaseous sulfur and hydrogen over a solid catalyst(heterogeneous reaction), wherein a sulfur melt is preferably providedat least in a lower region of the reactor into which gaseous hydrogen isintroduced. In the process, the reactant mixture may, for example, beintroduced from a reactant region into a limb of at least one U-shapedtube through at least one entry orifice arranged above the sulfur melt,passed along a flow path through the at least one U-shaped tube which ispartly in contact with the sulfur melt, and converted over a catalystarranged in a reaction region in the flow path. A product can be passedout of at least one exit orifice in another limb of the U-shaped tubeinto a product region (preferably separated from the reactant region).The H₂S synthesis is preferably performed in the reactor alreadydescribed.

The preferred process for synthesizing H₂S is performed in the reactorat temperatures of the reactant mixture and of the reactant regioncomprising the catalyst of from 300 to 450° C., preferably from 320 to425° C., more preferably from 330 to 400° C., which minimizes thecorrosion stress on the materials selected for the constructionelements. The temperature of the sulfur melt is preferably between 300and 450° C., especially between 320 and 425° C., preferably between 330and 400° C., more preferably between 350 and 360° C. The temperature inthe reactant space above the sulfur bath is preferably between 300 and450° C., especially between 320 and 425° C., preferably between 330 and400° C., more preferably between 350 and 380° C. The product mixturewhich exits from the reaction region into the product space preferablyhas a temperature between 300 and 450° C., especially between 320 and425° C., preferably between 330 and 400° C., more preferably between 350and 360° C. The pressures in the jacket space of the reactor and in theinterior of the U-shaped tubes are from 0.5 to 10 bar, preferably from0.75 to 5 bar, more preferably from 1 to 3 bar, most preferably from 1.1to 1.4 bar absolute.

The hydrogen introduced into the reactor in the preferred process ispreferably dispersed into the sulfur melt at a distributor deviceprovided in the lower section of the reactor. Firstly, the hydrogen isdistributed preferably by means of a distributor plate of thedistributor apparatus which is arranged horizontally within the reactorthrough the passage orifices provided therein from a hydrogen bubbleaccumulated below it into the sulfur melt present above the distributorplate. When there is inhibition of the passage of the hydrogen throughthe passage orifices, for example by sulfur deposited therein, thehydrogen bubble accumulates within the space defined by the distributorplate and the edge of the distributor device which extends downward, sothat, secondly, hydrogen is distributed by means of the edge region ofthe edge which extends downward into the sulfur melt surrounding it. Inthis case, hydrogen passes from the hydrogen bubble under thedistributor device through a gap between distributor device and reactorjacket into the sulfur melt present above the distributor device. Inthis way, it is ensured that the hydrogen is distributed within thesulfur melt in a sufficient amount during the continuous preparation ofH₂S.

The evaporation rate of the sulfur in the present invention is adjustedsuch that the reactant mixture comprises a sulfur excess. The excesssulfur is then fed out of the product region of the reactor with theproduct and subsequently separated out as a melt. This liquid sulfurcan, for example, be recycled via a collecting and divertingconstruction arranged in the upper subregion of the reactor, comprising,inter alia, a collecting tray and a return tube which proceeds therefromand is immersed into the sulfur melt, into the sulfur melt present inthe lower subregion of the reactor. The H₂S gases leaving the reactorare preferably cooled in a heat exchanger which serves as a cooler, theexcess sulfur being condensed out and passed back into the sulfur meltvia the collecting and diverting construction. The cooling medium usedmay be warm pressurized water in a secondary circuit.

In a preferred embodiment of the process according to the invention,this comprises the steps of

-   -   reacting gaseous sulfur and hydrogen over a solid catalyst in a        reactor with a sulfur excess to obtain an H₂S-containing crude        gas stream,    -   cooling the crude gas stream to from 114 to 165° C., preferably        from 127 to 163° C., more preferably from 135 to 161° C., in a        cooler to separate out excess sulfur and    -   passing the crude gas stream from the cooler into a vessel        comprising activated carbon.

In a preferred embodiment of the present invention, the sulfur collectedin the bottom of the vessel comprising the activated carbon is recycledinto the reactor via the cooler. To this end, a line is provided betweenthe cooler and the vessel comprising the activated carbon, through whichthe crude gas stream is passed in one direction from the cooler into thevessel and through which sulfur collected in the bottom of the vessel ispassed in an opposite direction from the vessel into the cooler. Thesulfur which forms in the vessel, for example in the decomposition ofH₂S_(x), runs out of the activated carbon (for example an activatedcarbon bed) and is collected in the bottom of the vessel. Thetemperatures in the vessel are selected such that the sulfur is liquidand can therefore flow into the bottom and from there into the line tothe cooler. The arrangement of a single line between the vesselcomprising the activated carbon and the cooler for conducting the cooledcrude gas stream in one direction from the cooler into the vessel andfor recycling sulfur in the opposite direction from the bottom of thevessel into the cooler in turn dispenses with flanges which mayconstitute possible leakage sites. The pipeline system is simplified.

The lines in the device which conduct liquid or gaseous sulfur,especially the line between the vessel comprising the activated carbonand the cooler, between reactor and cooler and/or the sulfur feed lineof the reactor, are preferably configured with gradients. Moreover,these lines are preferably designed with heating to from 100 to 170° C.A suitable method for this purpose is the use of jacketed lines or thewrapping of the lines with heatable corrugated tubes or electrical traceheating. Preference is given to using jacketed lines or corrugatedtubes. Suitable heating media in the jacket or in the corrugated tubeare, for example, steam or liquid water.

The invention will be illustrated in detail below with reference to thedrawing.

The drawing shows:

FIG. 1 a schematic illustration of a preferred embodiment of aninventive apparatus

The apparatus according to FIG. 1 is suitable for performing the processaccording to the invention. It comprises a reactor 1 for convertingsulfur and hydrogen, a cooler 40 connected to the reactor 1 for coolingan H₂S-containing crude gas stream passed out of the reactor 1 to from114 to 165° C., and a vessel 42 which comprises activated carbon 41, isconnected to the cooler 40 and has a bottom 43 for collecting sulfurwhich is obtained in the vessel 42 at from 114 to 165° C. from a crudegas stream comprising polysulfane. A line 44 is connected to the bottom43 of the vessel 42 and opens into the cooler 40 for the recycling ofsulfur (via the cooler 40) into the reactor 1.

The reactor 1 is closed with hoods 3, 4 at both ends of a cylindricalbody 2. At the upper hood 3, a product can be drawn off. At the lowerhood 4 is disposed a discharge stop 5 in order possibly to completelydischarge the contents of the reactor 1. In an upper section of thereactor 1, a plate 6 is provided, which separates an upper subregioncomprising a product region 7 from a lower subregion 8. The plate 6 isconnected to a reactor jacket 25 of the reactor 1. The lower subregion 8is filled partly with a sulfur melt 9 which is in contact via a phaseboundary with a reactant region 10 which is bordered at the top by theplate 6. The reactant region 10 comprises mainly gaseous hydrogen andsulfur.

The hydrogen is introduced into the sulfur melt 9 via a feed device 11into a lower section of the reactor 1, for example in the lower hood 4.The feed device 11 comprises a line 12 which runs obliquely and openslaterally into a tube 13 which is arranged vertically in the reactor 1and is open at the top and bottom. The upper end of the tube 13 projectsinto a space 14 which is bordered by a distributor device 15. Thedistributor device 15 comprises a distributor plate 16 arrangedhorizontally in the reactor 1 and an edge 17 which extends downward andhas a preferably serrated edge region 18. The hydrogen introduced viathe feed device 11 rises upward within the vertical tube 13 and collectsbelow the distributor plate 16 to form a hydrogen bubble. Passageorifices 19 in the distributor plate 16 disperse the hydrogen in thesulfur melt 9 present above it, and it rises upward in the form of gasbubbles within the sulfur melt 9, which strips sulfur out of the sulfurmelt 9. This forms a reactant mixture comprising gaseous hydrogen andsulfur in the reactant region 10 above the sulfur melt 9.

When the passage orifices 19 in the distributor plate 16 for hydrogenpassage are blocked, the hydrogen can also be dispersed from thehydrogen bubble accumulated below the distributor plate 16 via the edgeregion 18 into a gap 20 between the reactor jacket 25 and the edge 17 ofthe distributor device 15 into the sulfur melt 9.

Arranged within the cylindrical body of the reactor 1 are tubes 21 whichhave a U-shaped design. The U-shaped tubes 21 are connected to the plate6 by their two limbs 26, 27. The connection of the limbs 26, 27 to theplate 6 can be established by weld seam. The U-shaped tubes 21 areimmersed partly into the sulfur melt 9, which gives rise to thepossibility of direct heat exchange between the interior of the tubes 21and the sulfur melt 9 via the outer jacket surface 28 of the tubes 21.Within each U-shaped tube 21 is arranged a fixed catalyst bed 22 whichis provided in the two limbs 26, 27 of the U-shaped tubes 21.

As shown in FIG. 1, the distributor device 15 is connected to theU-shaped tubes 21, and a portion and especially the transition from onelimb 26 to the second limb 27 of the particular U-shaped tubes 21 runsbelow the distributor plate 16 through the space 14. Since this sectionof the U-shaped tubes 21 projects into the accumulated hydrogen bubbleand is not in direct contact with the sulfur melt 9, this section doesnot comprise any catalyst. The gap 20 is positioned between thedistributor device 15 and the reactor jacket 25. The distributor device15 is not connected directly to the reactor jacket 25.

In the reactor 1, the synthesis of hydrogen sulfide proceeds as follows.A reactant mixture passes from the reactant region 10 through one ormore entry orifices 23 arranged on the circumference of a limb 26 ofeach of the U-shaped tubes 21 into the interior of one limb 26 of theU-shaped tube 21, flows through the catalyst bed 22 present therein,which may be supplemented by an upstream inert bed, and is convertedsubstantially to hydrogen sulfide along the flow path within thereaction region comprising fixed catalyst bed 22.

The reactant mixture is converted in the reactor 1 at a pressure of from0.5 to 10 bar (most preferably from 1.1 to 1.4 bar) absolute, atemperature of from 300 to 450° C. and a sulfur excess. The sulfurexcess corresponds to a ratio of excess sulfur to hydrogen sulfideprepared of from 0.2 to 3 kg of sulfur per kg of hydrogen sulfideprepared.

The product passes out of the second limb 27 via at least one exitorifice 24 into the product region 7 and can be collected and dischargedfrom there via hood 3. As a result of the direct contact of the U-shapedtubes 21 with the sulfur melt 9, the heat of reaction released in theconversion to H₂S is released from the fixed catalyst bed 22 into thesulfur melt 9 via the outer jacket surface 28 of the U-shaped tubesalong the reaction region, and it is utilized for sulfur evaporation.

In order to keep the sulfur melt 9 at about the same height during theprocess, gaseous hydrogen and liquid sulfur are fed in appropriateamounts to the reactor 1 continuously via the feed device 11 and asulfur inlet 29.

Between the reactor 1 and the cooler 40 is arranged a first line 30which serves to pass the crude gas stream from the reactor 1 into thecooler 40 and to recycle sulfur in the opposite direction from thecooler 40 into the reactor 1. The liquid sulfur passes out of the firstline 30 to a collecting and diverting construction 45 arranged in theupper subregion of the reactor 1. This collecting and divertingconstruction 45 comprises a collecting tray 31, on which inlet stubs 34are arranged for passing the product from the product region 7 disposedbelow the collecting tray 31 into the product region 7 disposed belowit, and an edge 35. The liquid sulfur separated out is collected on acollecting tray 31 which is arranged horizontally in the product region7 of the reactor 1, and recycled via a return tube 32 immersed into thesulfur melt 9 into the sulfur melt 9 present in the lower subregion ofthe reactor 8. The reactor 1 is preferably insulated, so that the energyconsumption is at a minimum.

In the cooler 40, the H₂S-containing crude gas stream stemming from thereactor 1 is cooled from approx. 350° C. to from 114 to 165° C. Thiscondenses out excess sulfur, which passes through the first line 30 intothe reactor 1. In the cooler 40, conditions are present under whichpolysulfanes (H₂S_(x)) can form. From the cooler 40, an H₂S-containingcrude gas stream which comprises polysulfanes is passed through thesecond line 44 into the vessel 42 comprising the activated carbon 41.The second line 44 arranged between the vessel 42 comprising theactivated carbon 41 and the cooler 40 serves both for the passage of thecooled crude gas stream in one direction from the cooler 40 into thevessel 42, and for the recycling of sulfur in the opposite directionfrom the bottom 43 of the vessel 42 into the cooler 40.

The H₂S-containing stream purified by means of the activated carbon 41is discharged from the vessel 42 via a further line 33.

EXAMPLE

451 kg/hr of sulfur are introduced in liquid form at a temperature of144° C. into the jacket space of a tube bundle reactor. Simultaneously,28.2 kg/hr of hydrogen are introduced. The insulated tube bundle reactoris heated with an electrical trace heater which introduces 16 kW. Theheat losses through the insulation of the reactor are 4 kW. The sulfurin the reactor is at such a level that the reaction tubes, in theregions where they comprise catalyst, are surrounded by sulfur. In thesulfur bath, the nitrogen bubbling through is saturated with sulfur. Theheat needed for this purpose stems from the reaction tubes which aresurrounded by the sulfur bath. In the gas space, a temperature of 360°C. is present above the sulfur bath. The catalyst used is a Co—Mocatalyst on a support of alumina. The sulfur-laden hydrogen is passedinto the reaction tubes, where the conversion to hydrogen sulfide takesplace at a temperature of from 360 to 450° C. The catalyst loading is0.3 standard m³ of hydrogen/hr/kg of catalyst. At the walls of theapparatus, temperatures of from 350 to 380° C. are measured. Thepressure in the reactor is 1.2 bar absolute. The gas mixture whichleaves the reactor and consists of hydrogen sulfide, the excess sulfurvapors and of traces of unconverted hydrogen has a temperature of 358°C. The gas mixture which leaves the reactor is partly condensed in thedownstream heat exchanger. The hydrogen sulfide stream which leaves thecondenser has a temperature of 137° C. The condensed liquid sulfur whichis obtained at a temperature of 150° C. is recycled into the jacketspace of the reactor. 480 kg/hr of H₂S form with a purity of more than99.5% by volume. In the course of operation of the plant over a time of0.5 year, no changes in the parameters are needed to achieve a purity ofthe H₂S of 99.5% by volume. The energetic assessment of the reactor andof the partial condenser shows that 477 kg/hr of liquid sulfur aresimultaneously recycled from the partial condenser into the reactor. Theestablished ratio of recycled sulfur to hydrogen sulfide formed is 0.99kg of sulfur per 1 kg of hydrogen sulfide.

Reference numeral list 1 Reactor 2 Reactor body 3 Upper hood 4 Lowerhood 5 Outlet stub 6 Plate 7 Product region 8 Lower subregion of reactor9 Sulfur melt 10 Reactant region 11 Feed device for hydrogen 12 Line 13Tube arranged vertically 14 Space 15 Distributor device 16 Distributorplate 17 Edge 18 Edge region 19 Passage orifices 20 Gap 21 Tubes 22Fixed catalyst bed 23 Entry orifice 24 Exit orifice 25 Reactor jacket 26First limb 27 Second limb 28 Outer jacket surface 29 Sulfur inlet 30First line 31 Collecting tray 32 Return tube 33 Line 34 Inlet stub 35Edge 40 Cooler 41 Activated carbon 42 Vessel 43 Bottom 44 Second line 45Collecting and diverting construction

1.-9. (canceled)
 10. A process for preparing hydrogen sulfide H₂S byconverting a reactant mixture which comprises gaseous sulfur andhydrogen over a solid catalyst (22), which comprises converting thereactant mixture at a pressure of from 0.5 to 10 bar absolute, atemperature of from 300 to 450° C. and a sulfur excess in a reactor, thesulfur excess corresponding to a ratio of excess sulfur to H₂S preparedof from 0.2 to 3 kg of sulfur per kg of H₂S prepared, wherein thereactant mixture is obtained by passing gaseous hydrogen through asulfur melt (9) into a reactant region (10) of the reactor (1), thesulfur melt (9) having a temperature of from 300 to 450° C.
 11. Theprocess according to claim 10, wherein the catalyst (22) providedcomprises particles which comprise at least one element selected fromthe group of Ni, W, Mo, Co and V in oxidic or sulfidic form on a supportcomposed of alumina or silica.
 12. The process according to claim 10,wherein the conversion of the reactant mixture is performed in aone-stage reaction.
 13. The process according to claim 10, wherein heatof reaction which arises in the conversion of the reactant mixture isutilized for evaporation of the sulfur.
 14. The process according toclaim 13, wherein the heat of reaction is supplied to a sulfur melt (9)which provides sulfur for the reactant mixture by at least one of thefollowing processes: A) arranging the catalyst (22) in at least one tube(21), the reactant mixture being converted in the tube (21) and the tube(21) being partly in contact with the sulfur melt (9), B) heatinggaseous hydrogen via a heat exchanger by means of thermal energy of anH₂S-containing crude gas stream obtained in the reactor (1) in theconversion of the reactant mixture, and passing the heated hydrogenthrough the sulfur melt (9), and C) utilizing the thermal energy of theH₂S-containing crude gas stream obtained in the conversion of thereactant mixture by means of a heat exchanger to heat the sulfur melt(9).
 15. The process according to claim 10, wherein an H₂S-containingcrude gas stream passed out of the reactor (1) is cooled in a cooler(40) to separate out excess sulfur, and sulfur obtained in the cooler(40) is recycled into the reactor (1) for the preparation of H₂S. 16.The process according to claim 15, wherein a line (30) is providedbetween the cooler (40) and the reactor (1), through which, the crudegas stream is passed in a direction from the reactor (1) into the cooler(40) and through which the recycled sulfur is passed in an oppositedirection from the cooler (40) into the reactor (1).
 17. The processaccording to claim 15, wherein an H₂S-containing crude gas stream cooledby the cooler is passed through activated carbon (41) present in avessel (42) at a temperature between 114 and 165° C., and sulfurobtained is collected in the bottom (43) of the vessel (42).
 18. Anapparatus for continuously preparing hydrogen sulfide H₂S, comprising areactor (1) for converting a reactant mixture comprising gaseous sulfurand hydrogen over a solid catalyst (22) at a pressure of from 0.5 to 10bar absolute, a temperature of from 300 to 450° C. and a sulfur excesswhich corresponds to a ratio of excess sulfur to H₂S prepared of from0.2 to 3 kg of sulfur per kg of H₂S prepared, and a cooler (40) which isconnected to the reactor (1) and is for cooling an H₂S-containing crudegas stream passed out of the reactor (1) to condense at least a portionof the sulfur excess, a line (30) being arranged between the reactor (1)and the cooler (40) for passing the crude gas stream in a direction fromthe reactor (1) into the cooler (40) and for recycling sulfur in anopposite direction out of the cooler (40) into the reactor (1).